ALDL fuel pump testing?

[7Brandon07]

So I’m having problems getting fuel to my 1991 5.0L

I read that if I run 12v to the G pin on my ALDL that they fuel pump will turn on if it’s still good, my question is how do I do this ? Can’t seem to find information about that part, would I take a jumper wire stick it into a empty spot in my fuse black then stick the other end of the wire to the pin G on ALDL ? And if that is how I do it is that all I need to do ? And which spot on the fuse block would be ideal to use

the other thing is since I’ve owned the truck the battery has always seemed on the weak side to me, it will still crank my engine over and has always started my car up until this last Wednesday for about 9 months. It cranks my engine over but slowly car always started just now it don’t for not getting fuel dropped my battery off at the auto parts store there saying it tests bad, in the event my battery is bad could it be the reason behind me not getting fuel? I know in modern cars this definstely could be but mine is a 1991 thank you If anyone can give me any input on any of my questions I really need the truck and it couldn’t of happened at a worse time would really like to figure this out thanks

 

[7Brandon07]

Another thing I been pondering is If my oil pressure sending unit is bad could that keep my fuel pump from getting power ?

I don’t know if my oil pressure sensor is bad but I do know that my oil pressure gauge in my truck doesn’t work it sits at 30 and doesn’t change weather truck is running or not

 

[Oldblue98]

So I’m having problems getting fuel to my 1991 5.0L

I read that if I run 12v to the G pin on my ALDL that they fuel pump will turn on if it’s still good, my question is how do I do this ? Can’t seem to find information about that part, would I take a jumper wire stick it into a empty spot in my fuse black then stick the other end of the wire to the pin G on ALDL ? And if that is how I do it is that all I need to do ? And which spot on the fuse block would be ideal to use

the other thing is since I’ve owned the truck the battery has always seemed on the weak side to me, it will still crank my engine over and has always started my car up until this last Wednesday for about 9 months. It cranks my engine over but slowly car always started just now it don’t for not getting fuel dropped my battery off at the auto parts store there saying it tests bad, in the event my battery is bad could it be the reason behind me not getting fuel? I know in modern cars this definstely could be but mine is a 1991 thank you If anyone can give me any input on any of my questions I really need the truck and it couldn’t of happened at a worse time would really like to figure this out thanks

Does it try to start if you give it a little fuel down its throat ?

 

[7Brandon07]

Hello thanks for the reply yes if I put a little fuel down the tbi it will start but only for 2 or 3 seconds just long enough to burn that gas

 

[delta_p]

Another thing I been pondering is If my oil pressure sending unit is bad could that keep my fuel pump from getting power ?

I don’t know if my oil pressure sensor is bad but I do know that my oil pressure gauge in my truck doesn’t work it sits at 30 and doesn’t change weather truck is running or not

It shouldn't. The oil pressure switch is a backup to the fuel pump relay. It's there incase the relay fails while driving. If the relay works and the oil pressure comes up, the oil pressure switch closes and provides another power path to pump. So if you lose the relay while driving you can still get someplace as long as there is oil pressure.

 

[7Brandon07]

Oh thank you explained that pretty well, i understand how that works now, makes sense.

so i understand that it fuel pump doesn’t rely on the oil pressure switch like I was being led to believe it more or less is only but a back up in case the fuel pump relay fails. And even if the oil pressure switch had failed and ironically so did the fuel pump relay it would still run anyways once it builds pressure, so that’s not the culprit at all, I just need bite the bullet and accept I need to tow it to my friends house so I can drop that tank, it’s pretty lame living in a apartment complex I’ll be moving to a house though this week but with the truck taking a nap on me and no other vehicles. It’s quite the ordeal getting around anyways thanks

 

[delta_p]

And even if the oil pressure switch had failed and ironically so did the fuel pump relay it would still run anyways once it builds pressure,

Yeah the oil pressure switch is in a power path parallel to the relay. If the switch and relay failed like stated above, you could only run by applying direct power to the pump. What about checking the relay first before dropping the tank?

All the circuits are explained in the '91 service manuals if you want them https://www.gmt400.com/threads/88-95-service-manuals.43575/

 

[delta_p]

This too.

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[7Brandon07]

Thanks for the video I was thinking bout testing the relay but didn’t know how, something I did do I thought was weirs was I tested the fuel pump fuse with a test light it didn’t have any power. I can hear a relay click when I turn the key on but I’m not sure which one it is

 

[7Brandon07]

On Saturday I got around to working on the truck, it was the fuel pump truck runs a lot better with the new one I ended up dropping the tank was a bit of a pain n the ass to get it back up there doing it by myself n since my jack wouldn’t lift my truck very high off the ground come to find out my tank was a lot more full than the gauge lead me to believe it’s all done and good now though I however was not able to get the fuel filter off the nuts been pretty siezed anybody have any tips for that ? I was just using pb blaster. I think it’s been on there a while it’s actually a USA made filter